The principal goal of this project is to determine mechanistic features of the mitochondrial ATP synthase. This work is particularly relevant to cardiac tissue, which is almost completely dependent on the mitochondrial ATP synthase for aerobic synthesis of ATP. An understanding of the structure and function of the ATP synthase is essential before mitochondrial myopathies and pathologies that alter oxidative-phosphorylation can be completely understood and treated. This study will reveal important basic features of the ATP synthase. The ATP synthase is composed of a water soluble portion, the F-1 ATPase, and a membrane portion, F-0. The first aim it to purify, and crystallize either the mitochondrial F-1F-0 or F-1 after expression in yeast. This will provide molecular details into the mechanism of the ATP synthase and allow future studies that combine mutagenesis and biochemistry with crystal structural analysis. The second aim is to crystallize the co- complex of the bovine F-1 inhibitor protein (IF1) with bovine F-1 followed by crystal structural analysis. This will provide molecular details into the understanding of the mechanism of IF1 and the regulation of the ATP synthase. In total, these studies will provide a major advance in the understanding of the structure/function of the ATP synthase.